Food products based on wheat flour contain mixtures of different types of wheat grains and other cereals, either integral or otherwise. The importance of such products, particularly when these products are wheat flour tortillas, resides on the fact that said wheat flour tortillas economically compete with the already very popular corn dough tortillas for the preparation of various dishes, either at home, in restaurants and/or in fast food establishments, such as tacos with prepared food, burritos, quesadillas, Arabian bread or tacos, fajitas, bunuelos, chimichangas, etc.
In the present specification, the term "dough" or "masa" refers to the dough manufactured from refined or integral wheat flour, either containing or not other cereals and additives and either integral or refined. Similarly, the term "wheat products" refers to those products manufactured on the basis of refined or integral wheat flour, with or without other grains, cereals or additives. The term "tortillas" means flat and circular food products made from wheat flour dough with or without other grains or additives.
The wheat flour tortillas mainly contain the following ingredients: refined or integral wheat flour, water, edible oil and/or shortening or lard, salt and baking powder. Also, said products may contain additional flavoring agents, conditioners, emulsifiers, edible gums and preservers in order to improve the flavor, nutritional value, shelf life, texture, handling and appearance of the final product.
The current methods of preparation of wheat flour tortillas are well documented in the literature, with some of them being proprietary techniques. For instance, Serna-Saldivar et al, in Serna-Saldivar, S. O., Rooney, L. W., Wanisca, R. D., Cereal Foods World, 1988, Volume 33, Number 10, describes several methods of making wheat flour tortillas, one of them being the traditional manual shaping of the tortillas, which is carried out by the preparation of wheat dough balls with weights which depend on the desired size of the product. Before shaping the tortillas, the dough balls are permitted to rest for a period of time of from about 7 to about 20 minutes at a temperature of approximately 28.degree. C., in order to permit the activation of the baking powder and the conditioning of the gluten complexes in the dough. After the resting of the dough balls, said dough balls are extended manually by means of wooden, plastic and/or metallic rolls, previously coating the rolls with wheat flour in order to prevent the sticking of the dough to the roll and in order to facilitate the manipulation so as to obtain the traditional circular shape. The weight of the wheat flour tortillas varies between 15 and 35 grams and the moisture content in the raw wheat flour tortilla varies between approximately 45 and 55% by weight.
For cooking the tortillas, several methods are employed. The simplest one of said methods is a batch method which uses a comal that is a heated plate made from clay, metal or ceramics. The comal is heated at a temperature of from about 190.degree. C. to about 250.degree. C., depending on the type of the material of the comal, this method requiring that the cooking of the wheat flour tortilla be carried out on both sides of the product. When the tortilla is deposited for the first time on the hot comal, a first capping layer is developed with a thickness of several tenths of a millimeter, on the side which is in thermal contact with the comal. Normally the time for producing this capping layer is of from 15 to 30 seconds, depending on the temperature of the comal and the moisture content of the product. Then the wheat flour tortilla is turned over in order to carry out the cooking on the apposite side, which generally occurs within a period of time of from 15 to 30 seconds, and a second thin capping layer of several tenths of a millimeter is formed, both first and second capping layers having as their principal function to retain the water vapor.
The cooking time of the tortilla is completed when the product is puffed, inasmuch as the puffing of the tortilla is the indicator of a suitable cooking and in a certain way guarantees the necessary quality for the purposes of providing a suitable shelf life and good handling properties to the product.
Once the tortilla is cooked, the moisture content is reduced by 25 to 34% by weight. The productivity of the method depends on the amount of products able to fit on the comal at any given time, and on the thermal conductivity of the dough being cooked.
At the industrial and semi-industrial level, wheat flour tortillas are generally manufactured by using two main shaping methods: 1.--Hot-press and 2.--Die-cut.
In the hot-press method, the dough balls are prepared in special ball forming machines which feed said balls to an automatic hot press to give the tortilla its well-known flat and circular shape, by using in the hot plates of said presses temperatures of the order of between about 190.degree. C. to 220.degree. C., with pressing times of fractions of a second.
While shaping the tortilla by means of this pressing device, both sides of the tortilla entering into thermal contact with the hot plates, develop two thin capping layers of a thickness of tenths of a millimeter, which seal the tortilla to prevent water vapor exhaustion during the further cooking thereof, and the moisture content of the product is decreased in this stage by between 2 and 3% by weight.
In the die-cut method an extruding device is used for the shaping of a sheet of wheat dough having a suitable thickness, which is thereafter conveyed to a cutting system, having stamping disks in order to provide the circular shape characteristic of the wheat flour tortilla. Due to the fact that in the die-cut method the wheat dough contains less moisture, the thus produced tortillas are better fitted for the production of fried products.
The cooking of the tortillas produced by any one of the above described prior art methods, is carried out in a continuous manner by means of special cooking ovens, which are closed ovens containing conveyor belts to carry the tortillas. The ovens may be heated by the use of gas burners, hot air convection currents, electrical resistors, circulating hot air or by a combination of said means. For purposes of carrying out a suitable marketing of the products, the dimensions, weight and moisture content of the tortillas are kept similar to those obtained by the batch methods.
The temperature of the conveyor belts varies depending on the selected heating system, and generally in the commercial-type ovens, the conveyor belts are heated to a temperature of from about 190.degree. C. to 250.degree. C.
Depending on the temperatures selected for the cooking and on the thermal characteristics and dimensions of the dough, the cooking time for the wheat flour tortilla varies between about 60 and about 120 seconds, and the productivity of the industrial systems normally ranges from 2,500 to 30,000 wheat flour tortillas per hour, with a reduction of the moisture content after cooking to approximately 8 to 10% by weight.
Although these methods are satisfactory for producing the two indispensable capping layers of the wheat flour tortilla, the drawbacks that the moisture retention within the final product is deficient and that the capping layers of the wheat flour tortillas thus produced retain the same rough surface of the hot conveyor belts remain.
One other important problem of these prior art methods is the deficient thermal energy transfer from the hot surface to the product, thus resulting in a limited productivity, inasmuch as the low thermal conductivity of the dough and the amount of thermal energy used for carrying out the heating of the conveyor belt, renders this process slow and inefficient. The solutions proposed for increasing the efficiency of production include the installation of tandem feeding systems in order to increase the amount of products passing through the thermal cooking equipment per unit of time; the provision of means to increase the thermal energy transfer from the heating source to the product; or the design of more efficient ovens.
Some workers in the art have explored the use of microwave radiation for cooking the wheat dough with the purpose of solving the problem of direct contact heating from a comal or from a hot conveyor belt for manufacturing wheat flour tortillas. This method, however, excessively dries the shaped pieces of wheat dough, without satisfactorily cooking the outermost parts of the tortilla, thus producing a hard tortilla having inappropriate characteristics, namely, unattractive appearance, brittleness and absence of the characteristic flavor and color. Therefore, high frequency radiation has only been used for drying wheat flour products, but has been considered unsuitable for cooking wheat flour tortillas.
In order to try to solve the above problems, the present invention seeks to overcome the drawbacks shown by the prior art methods by means of the use of a method which permits to cook wheat flour products by using infrared radiation without unduly drying the same.